The "gotcha" that I've run into when swapping cassette bodies around is that the "mountain" hub shells have a slight recess for the cassette body where the "road" hubs do not- the right surface of the hub shell is flat (ish).

I had this bite me when the 8-speed cassette body I had combined with an old Deore XT shell failed while on tour in Canada. The tour's mechanic was able to get a replacement body at the next town (he loaned me a wheel so I could finish the day), but it was a "road" cassette body. It goofed up the indexing a bit, and the rear derailleur cage "tinked" on the spokes in low gear. No huge problem, but I avoided using the big cog for the rest of the tour.

This may not be the case with all Shimano hubs, but it is something to look out for.